fix NAR n-step prediction across estimators

[wilsonrljr]

• compute exact block horizons without internal padding
• reuse shared NAR step-ahead logic in General NARX and NARXNN
• validate step sizes and preserve fractional predictions for integer NAR data
• cover partial blocks, bias modes, shared consumers, and Array API fallback

[codacy-production]

Not up to standards ⛔

🔴 Issues 30 high

Alerts:
⚠ 30 issues (≤ 0 issues of at least minor severity)

Results:
30 new issues

Category	Results
Security	30 high

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🟢 Metrics 42 complexity · -3 duplication

Metric	Results
Complexity	42
Duplication	-3

View in Codacy

🟢 Coverage 95.45% diff coverage · -0.02% coverage variation

Metric	Results
Coverage variation	✅ -0.02% coverage variation (-1.00%)
Diff coverage	✅ 95.45% diff coverage

View coverage diff in Codacy

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (5adc2e7)	5622	5553	98.77%
Head commit (f80646e)	5613 (-9)	5543 (-10)	98.75% (-0.02%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#244)	22	21	95.45%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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